premium pixels is one of my favourites because when Orman Clarke says they are free, he means it,just search for the free items, and there is no funny pricing or linking to envato. the site is easy to use, and while the quantity of free items is small, the quality is fantastic.

icon finder is great because again you can limit to free icons, some of the paid ones are only about $1. they have a nice amount of modern flat design icons, and in various formats such as ico, png and svg